2015-03-31 I&S Committee - Item 5 - Attachment 1 - Munna Pt Bridge Repairs Level 3 Bridge Report

4.0 Repair Options – Cost Comparison

Doing nothing is not an option. TMR identified the main issues in 1999, and unfortunately
no repair action has been taken since then.

It is extremely fortunate that the bridge has dilapidated slower than expected. This gives
Council enough time to respond in a planned fashion, and spread the repair/maintenance
cost over the next 3-5 years.

There are effectively two options to compare: 1) Construct the new substructure
designed by Arup, which would provide wider headstocks that could be used to widen the
bridge in the future; or 2) repair the existing bridge, which could also be widened in the
future when money becomes available. Construction of a new bridge is not a realistic
option, because construction would require the bridge crossing to be shut down for 18
months or more. Repairs need to commence NOW. We compare the two options in the
following table.

Table 1: Cost Comparison of New substructure versus repairing the existing bridge
Option 1) – Construct new substructure Option 2) – Repair the existing bridge.
under bridge, as designed by Arup. 50 50-year life if maintenance schedule is
year deck life & 100 year substructure life properly followed. This option makes no
(if maintenance schedule is properly special allowance for sea level rises or
followed). From our review of the design associated canal erosion
report for this option, it appears that there
is no special allowance for sea level rises
or associated canal erosion.
Works to be carried out: Install new piles Works to be carried out: Install extra 6
and pilecaps just outside existing bridge columns; break out cracked and drummy
footprint.    Construct     new     columns. concrete in pilecap beams and repair;
Construct longer, larger headstocks that install cathodic protection to pilecap beams
envelop existing headstocks. Demolish (50yr life); coat pilecap beams with silane;
existing columns, pilecap beams and strengthen and encase all piles using
existing piles down the bed level.            galvanised reo and Portland: flyash
                                              blended concrete; spray waterproofing
                                              compound over deck; install plastic lining in
                                              scuppers; replace deck joints; coat
                                              headstocks, columns, abutments and
                                              underside + sides of deck with protective
                                              silane. Clean up and coat all stressing bar
                                              ends.




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